Both the ServeUntilRecachedPolicy and EagerRecachePolicy use a timestamp to determine if objects should be refreshed. However the flushpolicies
(EagerRecacheFlushPolicy and NotifyFlushListeningPolicy) they use store the timestamp in the config workspace under the advanced-cache module.

There is only one timestamp there, so the timestamp is global for all caches configured with that policy so this does not work in multisite configurations or on single site with multiple cache configurations.