Currently CheckMetadataConsistency only checks CollectionShardingState and DatabaseShardingState entries of namespaces reachable through either the global or the local collection catalogs; other entries are never checked. Therefore we are missing validation that no stale CSS/DSS entries are left.

For example, after dropping a database, we are missing validation that there are no CSS/DSS entries stating that collections on that database exist.

Proposal:
For all shards, and all their replicas, scan all the entries on the CSS and DSS and validate them.