You have a couple of options. The first one I'd suggest is to use CROSSCHECK to remove any backups that no longer exist. The RMAN command is:
There are other options, so consult the RMAN Reference Guide. The CROSSCHECK command does not remove the backups from RMAN. It marks backups as AVAILABLE, UNAVAILABLE, or EXPIRED. You can use the DELETE EXPIRED command to remove the expired backups.
Another thing that you should consider doing is using the DELETE OBSOLETE command on a regularly scheduled basis. This can remove those backups from RMAN that are no longer needed for recovery.
Finally, to change the status of an RMAN backup, use the CHANGE command. For instance, to change backupset #1234 to UNAVAILABLE, use the following command:
CHANGE BACKUPSET 1234 UNAVAILABLE
This was first published in September 2004