1. An apparatus located in a first region of a system, the apparatus comprising: a memory configured to store database updates performed on a first database cluster in the first region, wherein each database update corresponds to a key, and a first invalidation associated with the key is appended to the update; a processor configured to: when a replica database in a second region remote from the first region has failed and cannot respond to database updates, publish a first subset of the first invalidations to a subscriber in the second region, wherein the first subset of the first invalidations are associated with keys having values stored in the replica database, wherein the subscriber is configured to send the first subset of the first invalidations to caches in the second region to cause values stored in the caches for the keys to be deleted.