If the tapes are in scratch then there are no images on the tape, so a "bpmedialist -m " will say the tape is not in the media db. Then you can just delete the tape from scrach (delete within the Admin Console), "vmquery -m " should now show no entry for the meida.
The other way to do it is to move the tapes into a new pool, which you can name accordingly, such as "bad media".
