Give it a day or two. If the problem still persists or you can try it now, check this out: http://forums.comcast.com/t5/Basic-Internet-Connectivity-And/How-to-Flush-your-local-DNS-cache/td-p/594989.
You can wait, or do it now, but it should be fine in a day or two. It really depends on Comcast and what's going on behind the scenes.