diff --git a/packages/backend/src/core/FederatedInstanceService.ts b/packages/backend/src/core/FederatedInstanceService.ts
index 662c7f7f2d..eb634b1d68 100644
--- a/packages/backend/src/core/FederatedInstanceService.ts
+++ b/packages/backend/src/core/FederatedInstanceService.ts
@@ -5,21 +5,24 @@
 
 import { Inject, Injectable, OnApplicationShutdown } from '@nestjs/common';
 import * as Redis from 'ioredis';
-import type { InstancesRepository } from '@/models/_.js';
+import type { InstancesRepository, MiMeta } from '@/models/_.js';
 import type { MiInstance } from '@/models/Instance.js';
-import { MemoryKVCache, RedisKVCache } from '@/misc/cache.js';
+import { MemoryKVCache } from '@/misc/cache.js';
 import { IdService } from '@/core/IdService.js';
 import { DI } from '@/di-symbols.js';
 import { UtilityService } from '@/core/UtilityService.js';
 import { bindThis } from '@/decorators.js';
+import type { GlobalEvents } from '@/core/GlobalEventService.js';
+import { Serialized } from '@/types.js';
+import { diffArrays } from '@/misc/diff-arrays.js';
 
 @Injectable()
 export class FederatedInstanceService implements OnApplicationShutdown {
-	public federatedInstanceCache: RedisKVCache<MiInstance | null>;
+	private readonly federatedInstanceCache: MemoryKVCache<MiInstance | null>;
 
 	constructor(
-		@Inject(DI.redis)
-		private redisClient: Redis.Redis,
+		@Inject(DI.redisForSub)
+		private redisForSub: Redis.Redis,
 
 		@Inject(DI.instancesRepository)
 		private instancesRepository: InstancesRepository,
@@ -27,30 +30,15 @@ export class FederatedInstanceService implements OnApplicationShutdown {
 		private utilityService: UtilityService,
 		private idService: IdService,
 	) {
-		this.federatedInstanceCache = new RedisKVCache<MiInstance | null>(this.redisClient, 'federatedInstance', {
-			lifetime: 1000 * 60 * 30, // 30m
-			memoryCacheLifetime: 1000 * 60 * 3, // 3m
-			fetcher: (key) => this.instancesRepository.findOneBy({ host: key }),
-			toRedisConverter: (value) => JSON.stringify(value),
-			fromRedisConverter: (value) => {
-				const parsed = JSON.parse(value);
-				if (parsed == null) return null;
-				return {
-					...parsed,
-					firstRetrievedAt: new Date(parsed.firstRetrievedAt),
-					latestRequestReceivedAt: parsed.latestRequestReceivedAt ? new Date(parsed.latestRequestReceivedAt) : null,
-					infoUpdatedAt: parsed.infoUpdatedAt ? new Date(parsed.infoUpdatedAt) : null,
-					notRespondingSince: parsed.notRespondingSince ? new Date(parsed.notRespondingSince) : null,
-				};
-			},
-		});
+		this.federatedInstanceCache = new MemoryKVCache(1000 * 60 * 3); // 3m
+		this.redisForSub.on('message', this.onMessage);
 	}
 
 	@bindThis
 	public async fetchOrRegister(host: string): Promise<MiInstance> {
 		host = this.utilityService.toPuny(host);
 
-		const cached = await this.federatedInstanceCache.get(host);
+		const cached = this.federatedInstanceCache.get(host);
 		if (cached) return cached;
 
 		let index = await this.instancesRepository.findOneBy({ host });
@@ -73,7 +61,7 @@ export class FederatedInstanceService implements OnApplicationShutdown {
 			index = await this.instancesRepository.findOneByOrFail({ host });
 		}
 
-		await this.federatedInstanceCache.set(host, index);
+		this.federatedInstanceCache.set(host, index);
 		return index;
 	}
 
@@ -81,7 +69,7 @@ export class FederatedInstanceService implements OnApplicationShutdown {
 	public async fetch(host: string): Promise<MiInstance | null> {
 		host = this.utilityService.toPuny(host);
 
-		const cached = await this.federatedInstanceCache.get(host);
+		const cached = this.federatedInstanceCache.get(host);
 		if (cached !== undefined) return cached;
 
 		const index = await this.instancesRepository.findOneBy({ host });
@@ -109,8 +97,35 @@ export class FederatedInstanceService implements OnApplicationShutdown {
 		this.federatedInstanceCache.set(result.host, result);
 	}
 
+	private syncCache(before: Serialized<MiMeta | undefined>, after: Serialized<MiMeta>): void {
+		const changed =
+			hasDiff(before?.blockedHosts, after.blockedHosts) ||
+			hasDiff(before?.silencedHosts, after.silencedHosts) ||
+			hasDiff(before?.mediaSilencedHosts, after.mediaSilencedHosts) ||
+			hasDiff(before?.federationHosts, after.federationHosts) ||
+			hasDiff(before?.bubbleInstances, after.bubbleInstances);
+
+		if (changed) {
+			// We have to clear the whole thing, otherwise subdomains won't be synced.
+			this.federatedInstanceCache.clear();
+		}
+	}
+
+	@bindThis
+	private async onMessage(_: string, data: string): Promise<void> {
+		const obj = JSON.parse(data);
+
+		if (obj.channel === 'internal') {
+			const { type, body } = obj.message as GlobalEvents['internal']['payload'];
+			if (type === 'metaUpdated') {
+				this.syncCache(body.before, body.after);
+			}
+		}
+	}
+
 	@bindThis
 	public dispose(): void {
+		this.redisForSub.off('message', this.onMessage);
 		this.federatedInstanceCache.dispose();
 	}
 
@@ -119,3 +134,9 @@ export class FederatedInstanceService implements OnApplicationShutdown {
 		this.dispose();
 	}
 }
+
+function hasDiff(before: string[] | null | undefined, after: string[] | null | undefined): boolean {
+	const { added, removed } = diffArrays(before, after);
+	return added.length > 0 || removed.length > 0;
+}
+
diff --git a/packages/backend/src/core/entities/UserEntityService.ts b/packages/backend/src/core/entities/UserEntityService.ts
index 56506a5fa4..feddb8fa94 100644
--- a/packages/backend/src/core/entities/UserEntityService.ts
+++ b/packages/backend/src/core/entities/UserEntityService.ts
@@ -609,7 +609,7 @@ export class UserEntityService implements OnModuleInit {
 			requireSigninToViewContents: user.requireSigninToViewContents === false ? undefined : true,
 			makeNotesFollowersOnlyBefore: user.makeNotesFollowersOnlyBefore ?? undefined,
 			makeNotesHiddenBefore: user.makeNotesHiddenBefore ?? undefined,
-			instance: user.host ? this.federatedInstanceService.federatedInstanceCache.fetch(user.host).then(instance => instance ? {
+			instance: user.host ? this.federatedInstanceService.fetch(user.host).then(instance => instance ? {
 				name: instance.name,
 				softwareName: instance.softwareName,
 				softwareVersion: instance.softwareVersion,
diff --git a/packages/backend/src/misc/cache.ts b/packages/backend/src/misc/cache.ts
index 48b8f43678..a6ab96c189 100644
--- a/packages/backend/src/misc/cache.ts
+++ b/packages/backend/src/misc/cache.ts
@@ -308,8 +308,17 @@ export class MemoryKVCache<T> {
 		}
 	}
 
+	/**
+	 * Removes all entries from the cache, but does not dispose it.
+	 */
+	@bindThis
+	public clear(): void {
+		this.cache.clear();
+	}
+
 	@bindThis
 	public dispose(): void {
+		this.clear();
 		clearInterval(this.gcIntervalHandle);
 	}