There is no reason currently to replicate expiration commands across site.

Lifespan will work just fine without without replicating as the entry is expired on either side properly, irrespective of system clocks.

However max idle doesn't support the given semantics with xsite. We currently only confirm from other nodes in the same cluster for max idle before removing. It would be extremely costly to query all the cross sites to see if they have a read on the same entry before expiring. Also this requires having system clocks somewhat close in time, which can be even more problematic with clusters in disparate locations. We need to document that this doesn't work as well.