Have you actually tried? I did, and it's the way as Oracle says:
To determine whether backups stored on disk or tape exist. Backups are either backup sets or media-managed proxy copies.
The crosscheck command checks only backup sets marked AVAILABLE or EXPIRED, either by examining the backup pieces on disk when the channel is type disk, or by querying the media manager when the channel is type 'sbt_tape'. It only processes backups created on the specified channel.
RMAN does not delete any backup pieces that it is unable to find, but updates their repository records to EXPIRED status. If some backup pieces were erroneously marked as EXPIRED, for example, because the media manager was misconfigured, then after ensuring that the files really do exist in the media manager, run the crosscheck backup command again to restore those files to AVAILABLE status.
"Maintaining the RMAN Repository".
Execute crosscheck backup only at the RMAN prompt.
Allocate a maintenance channel before issuing crosscheck backup.
allocate channel d1 type disk;
sql 'alter system archive log current';
release channel d1;
allocate channel for maintenance type disk;
change archivelog until time 'sysdate-1' delete;
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