In 2018 I wrote an internal (Check Point) unofficial ATRG that covers Domain Objects in a lot more detail than sk120633 covers. I've discussed this document with our developers and confirmed all the details and was given permission to share this on CheckMates!
The attached document contains basic info on types of domain objects, Information on how domains are looked up and how often, cache of results, and troubleshooting steps with some API to confirm your usage.
This has since been updated to show the changes in 80.20 where the service, in my opinion, is super optimized and awesome!
Thanks for reading!