How do I "flush" my DNS/web services so that it sees the updated website like everyone else?
if you go into a terminal window and type:

ping [DNS name of site]


What does it give you? Now do the same on your roommate's PCs from a command prompt.

if you do it with a hostname rather than IP address ping gives you the IP address and the FQDN of the site. They should be the same on both/all computers. If they are then Safari/Chrome has cached some data and is stubbornly holding onto it. So empty the caches on both and try again.

If it is different on your Mac then there is a cache somewhere that will not reset. You could try the command again, followed by a reboot and possibly even one of the cleaning utilities (like Onyx) followed by a reboot and see what that does.