Parse domain from URL

Hey guys, I'm faced with an interesting problem, and wondering if there's an easy solution. I need to strip out a domain name from a URL, and ignore subdomains (like www) I can use parse_url to get the hostname. And my first thought was to take the last 2 segments of the hostname to get the domain. So if the URL is http://www.example.com/ Then the domain is "example.com." If the URL is http://example.org/ then the domain is "example.org." This seemed to work perfectly until I come across a URL like http://www.example.co.uk/ My script thinks the domain is "co.uk." So I added a bit of code to account for this, basically if the 2nd to last segment of the hostname is "co" then take the last 3 segments. Then I stumbled across a URL like http://www.example.com.au/ So it occurred to me that this is not the best solution, unless I have a definitive list of all exceptions to go off of. Does anyone have any suggestions? Any advice is much appreciated. Thanks, Brad