I'm not aware of a data store which populates its replicas with data from a cache. Surely there are caches within any given data store, but the whole point of a replica is to have the data replicated (for scaling reads, redundancy in case your leader fails).

If you're using caches, you're deliberately sending old data to the replicas. I can't think of why you'd do that. I guess you could have replicas of your caches, but I'm referring specifically to data store replicas.