DNS on private network

[Rodrigo Sanchez Re]

Hi,
	I have a DNS server on a private network. It Server is authoritative
for our private domain and it has some forward zone for other Internals
domains,  configurated on others DNS. So all the queries that It can't
resolve itself or through of the forward zone, defined on it, are being sent
to a root-nameserver to look for a answer from it. But I don't wish resolve
queries for other domains don't defined. So, how can I do for DNS don't make
queries to a roots-nameserver for domain don't defined on our DNS as master
o forward zone?; I tried to remove "hint zone" but didn't work.
	Thanks in advance

Rodrigo Sánchez Ré