Nostr note immutability presents some interesting challenges. The only way to update data is to replace it, and somehow tell every client they need to use a new source of truth.
Nostr is like Lisp but for Internet protocols.
Discussion
The obvious way to do something like this is to publish a note that references notifications to be cleared by their unique address. It should be "invisible" and not show up on user-facing feeds. It's only effective if multiple clients respect that note though.