You can do what mixx said, or:
If you're on IE:
go into options, and do the following:
clear temp files
all three of those are on the first menu.
then, I can't remember off the top of my head, having been in IE for a while, i think you go to content, then to AutoComplete, and clear all of those. That will clear any searches you have done.
And if you're in mozilla:
Just go into options, click on privacy, and select the clear all box.
\o/ only one command.