I believe you can get this if you setup the underlying disks with dm-integrity, though I’m not sure it’s really worth it since it’s a very manual setup and has lots of potential edge cases and performance issues. Basically when the underlying disks are setup with dm-integrity, each read is verified with a checksum, if the checksum doesn’t match, the dm-integrity layer will return a read error and mdadm will log an error and automatically fallback to the secondary mirror. A “scrub” in this case would simply be reading the disk to /dev/null with dd, then checking the mdadm logs for any errors.

Note that it’s been a long time since I’ve messed with this, so it’s possible I got the exact details of the setup wrong.