Proxy a domain from one server to another and retain domain name

Question

I have a single external address that points to a server that is serving multiple domains using virtual hosts. I would like to serve one of the virtual hosts on a new physical machine and am trying to use a reverse proxy to make this happen.

On the main server the configuration looks like this (names changed to protect the guilty):

<VirtualHost *:80>
    DocumentRoot /abc/htdocs/virtual/swnc
    ServerName swnc.org
    <Directory "/abc/htdocs/virtual/swnc">
        Options FollowSymLinks MultiViews
        AllowOverride None
        Order allow,deny
        Allow from all
    </Directory>
</VirtualHost>

On the new physical machine I have the domain referenced above configured with:

<VirtualHost *:80>
    ServerName swnc.org
    ProxyPass "/" "http://www.example.org/virtual/swnc"
    ProxyPassReverse "/" "http://www.example.org/virtual/swnc"
</VirtualHost>

This configuration works but the resulting URL is what is specified in the ProxyPass statement above rather than the "real" URL which should be swnc.org.

I tried adding ProxyPreserveHost On in the configuration but it did not make any difference. Is there something I am missing or is it simply not possible to proxy the request to the new machine and retain the "real" domain name?

Update:

Here are the Apache configuration files on the old server and the new server using the suggestions from Stephen's answer.

Old Server

<VirtualHost *:80>
    ServerName ncdrought.org
    ProxyPass "/" "http://new.ncdrought.org"
    ProxyPassReverse "/" "http://new.ncdrought.org"
</VirtualHost>

New Server

<VirtualHost *:80>
    ServerName   new.ncdrought.org
    DocumentRoot /var/www/ncdrought.org
    <Directory "/var/www/ncdrought.org">
    Options FollowSymLinks
    AllowOverride All
    Require all granted
    </Directory>
</VirtualHost>

Answer 1

The proxy directives have to go on the the old machine. The machine that is acting like the pass-through needs to be configured as the proxy.

On your new machine, you need to set it up with a different host name, like a sub-domain, .local domain, or IP address that can be accessed on your internal network.

So the configuration should like like this:

old machine

<VirtualHost *:80>
    ServerName swnc.org
    ProxyPass "/" "http://swnc-backend.local/"
    ProxyPassReverse "/" "http://swnc-backend.local/"
</VirtualHost>

new machine

<VirtualHost *:80>
    DocumentRoot /abc/htdocs/virtual/swnc
    ServerName swnc-backend.local
    <Directory "/abc/htdocs/virtual/swnc">
        Options FollowSymLinks MultiViews
        AllowOverride None
        Order allow,deny
        Allow from all
    </Directory>
</VirtualHost>