chunk down - dbspace isn't ???

I'm trying to following some instructions Tech Support gave me for testing backup/recovery. Procedure is to backup system, intentionally corrupt a chunk and then restore the chunk from backup. I've successfully (sic) corrupted the chunk but the dbspace is still marked up. The instructions say (earlier steps omitted): 7. Force related dbspace down: onmode -o". 8. Check that dbspace is now flagged as down: "onstat -d" 9. Allow system to checkpoint with down dbspaces: "onmode -O" 10. Initiate warm recovery of dbspace: "onbar -r chunk1" 11. Backup current logical log: onbar -l -c "onmode -o" (step 7) doesn't work. What is the proper way to mark a dbspace down if it doesn't realize it contains a corrupted chunk? Thanks, Carrie Coy