I created a test domain in MAAS DNS to see if I could delegate the zone to Openstack Designate (which didn’t work by the way).
When I try delete the domain it fails with error
("Cannot delete some instances of model 'Domain' because they are referenced through a protected foreign key: 'DNSResource.domain'", <QuerySet [<DNSResource: name=record>]>)
The only way I’ve managed to get rid of it is to go into the postgresql maasdb and manually remove the rows from the maasserver_dnsresource table
It appears that even though the GUI says the records were deleted, it leaves behind protected phantom objects in the database.