Apache URL rewrite peculiar case

Hi All,

I have a generic website name eg: main.example.com. This website due
to load balancing points to server server1.example.com. Now,
server1.example.com processes the request and gives the output. The
output is of form http://server1.example.com/xyz. I want the processed
output to show as
http://main.example.com/xyz and not http://server1.example.com/xyz

How can this be done? Any clues

Thanks in Advance
Jaysheel