reverse query question

[Vu Pham ( Sivell )]

Hi all,

There is something I misunderstand for reverse queries ( from ip address to
hostname ).

A dns server ( for domain mydomain.net ) has reverse zone file containing
pointers for ip from 192.168.1.1 to 192.168.1.127,
Another dns server ( for domain sub.mydomain.net )  has reserve zone file
coning pointers for ip from 192.168.129  to 192.168.254.

Then, a query coming to the first dns server asks for hostname of
192.168.1.200.
How can the first dns server knows that it must ask the 2nd one for the
answer ?

Thanks for your help , and sorry for my English.

Vu Pham