So shards quickly pick up a new shard key, after refineCollectionShardKey updates the metadata for a collection, it should trigger refreshes on each shard that contains chunks for the refined collection. This isn't necessary for correctness, so triggering the refreshes can be best-effort and refineCollectionShardKey should return without waiting for each refresh to complete.

SERVER-42369 tracks the work to guarantee these refreshes are eventually triggered.