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.

Not really. Replicas are constantly replicating live data from your leader. All of it, in its raw form. A query against a replica isn't inherently faster than a query against the leader, the data is likely just a bit old.

A cache stores the output of an operation to avoid needing to perform the same operation again. You deliberately put data into a cache to avoid needing to create that data a second time—it won't magically appear there.