Hello Mark Drucker1,
Thank you for posting in Microsoft Community forum.
Sites are divided by subnet segments. You can put DCs (DNS servers) you select to the corresponding sites.
If all the domain devices of user endpoints belong to correct subnet segments, then the devices and users should find the correct DC and DNS region.
Creating a Site Design | Microsoft Learn
Designing the Site Topology | Microsoft Learn
I hope the information above is helpful.
If you have any question or concern, please feel free to let us know.
Best Regards,
Daisy Zhou