LinuxQuestions.org - 2 proxy servers in front of an application

I am having a website which is being served on my LAN as http://internal1.mydomain.com the vhost configuration for this is

Code:

ServerAdmin webmaster@localhost

 ServerName internal1.mydomain.com 

ProxyRequests Off 

        <Proxy *>

        Order deny,allow

        Allow from all

        </Proxy>

ProxyPreserveHost On 



ProxyPass / http://localhost:9090/ 

ProxyPassReverse / http://localhost:9090/

it is working very fine on LAN. I am able to use my application completely from LAN.

There is another server which is having public IP and I want this website to be available on internet.

A request for public domain comes as

http://www.mypublicdomain.com/something

How do I transfer that internally so that it reaches or is being served by http://internal1.mydomain.com
Is it possible to change the ServerName of an HTTP Request in Apache2
if yes then how?