My network exists in private address space and I am unable to perform DNS lookups against DNS servers on the internet directly (blocked by firewall). There are other networks that exist in the same private address space as my network. I need to be able to perform DNS lookups for devices in these networks as well.

There are 2 main internal DNS servers in this private address space, but not on my netowrk. I can perform DNS lookups against both of these servers for devices internal to our address space and names on the internet. I would like to permanently remove the root hints from our Server 2008 R2 DNS server and replace them with these 2 internal DNS servers. I have removed them from the dnsmgmt console, the C:\Windows\System32\DNS\cache.dns file, and from the RootDNSServers folder under the System folder in ADUC. Even so, they continue to repopulate into the root hints tab in the server properties for DNS after roughly an hour. Does anyone know how to permanently remove these entries?