ZFS destroy snapshot does not work

[Willem Jan Withagen]

Hi,

Probably due to too many reboots when the system was livelocked.
But now I have the following problem.

/sbin/zfs destroy -r zfsraid/backups at Monday
cannot destroy 'zfsraid/backups at Monday': dataset does not exist
no snapshots destroyed
/sbin/zfs snapshot -r zfsraid/backups at Monday
cannot create snapshot 'zfsraid/backups at Monday': dataset is busy
no snapshots were created

/sbin/zfs destroy -r zfsraid/home@$DATE
cannot destroy 'zfsraid/home at Monday': dataset does not exist
no snapshots destroyed
/sbin/zfs snapshot -r zfsraid/home at Monday
cannot create snapshot 'zfsraid/home at Monday': dataset is busy
no snapshots were created

Where this used to work(tm)....

I can iterate over all filesystems and then destroy/create a backup.

Except for one:
# zfs list -r zfsraid/home/trouble
NAME                          USED  AVAIL  REFER  MOUNTPOINT
zfsraid/home/trouble          149G  3.49T   148G  none
zfsraid/home/trouble at Sunday  1.06G      -   148G  -

# zfs destroy -r zfsraid/home/trouble
cannot destroy 'zfsraid/home/trouble at Sunday': dataset already exists
Exit 1
# zfs destroy zfsraid/home/trouble at Sunday
cannot destroy 'zfsraid/home/trouble at Sunday': dataset already exists
Exit 1
# zfs destroy -r zfsraid/home/trouble at Sunday
cannot destroy 'zfsraid/home/trouble at Sunday': snapshot is cloned
no snapshots destroyed

But of this last fact I do not remember cloning anything. Nor can I find 
any suggestions as to the filesystem being cloned.....

So how do I get ride of this rouge filesystem.

There is something like zdb, but the manual page is purposely vague on 
how to use that...

Thanx,
--WjW