When the PPM policy is created the domain is there by default, but it's an issue that you can't find it again once its removed. Therefore you the PPM Policy is recreated the domain will be there.
Another option would to link the PPM GPO to the root is via native GPMC
Since the PPM policy is a GPO you can scope it natively as well as through the Product. Also since its a GPO you must scope a group as well as OU in order for the GPO to be enforced.