New ip won't update

[Ken Williams]

Picture 3 servers on the same ISP/network, server 1 had test.com.  I updated 
the internic to have test.com point to server 2 - eveything is good, test.com 
on the internet now resolves to server 2.  But server 3 still thinks test.com 
is at server 1.  Its a TTL or caching problem?  But when or why or what do I 
have to change on server 3 to make it "reset" itself so it does a real lookup 
for test.com, not just get whatever it thinks it is.

Thanks