[Samba] Cleanup after site deleted

[Roy Eastwood]

Some time ago I created two sites in AD using RSAT tools.    Recently the need for these separate sites has gone, so I removed all
the servers and workstations etc from these sites and put them back into 'Default-First-Site-Name' and deleted the sites.   I have
just noticed that the DNS Manager is still showing one of the sites remaining (the other has disappeared).   Whilst it is possible
to delete the individual entries, the site hierarchy remains, and attempting to delete the <site-name> using DNS Manager results in
"The DNS domain cannot be deleted.   This function is not supported on this system.".  For example:

<server>
|_Forward Lookup Zones
     |_<dns-domain>
         |_ _sites
             |_<site-name>
             |   |_ _tcp
             |
             |_Default-First-Site-Name


etc.      Shouldn't samba clean up after itself?     How can this be cleaned up manually?

Many thanks,

Roy