Why is Safari displaying scrambled graphics?
Solution 1:
This isn't so much a Safari problem as it is an OS X / hardware one. I'm going to guess that you have Intel or Nvidia graphics on a MacBook (Pro).
It's well-documented; there are lots of people with these issues (including myself). As far as I've found, you can't fix it. Just restart or wait it out.
Sorry I can't be more useful.