This directive is only useful for Apache proxy servers within intranets. The ProxyDomain directive specifies the default domain which the apache proxy server will belong to. If a request to a host without a domain name is encountered, a redirection response to the same host with the configured Domain appended will be generated.
Example:
ProxyRemote * http://firewall.mycompany.com:81 NoProxy .mycompany.com 192.168.112.0/21 ProxyDomain .mycompany.com