I knew this - but forgot and instead of spinning my wheels when I make the same mistake in a month, I figured I'd quickly blog it to help me remember.
Don't forget when you cfdump the CGI scope, you are getting what is basically a "known" set of CGI variables. There may be additional CGI values available that will not show up.
A good example of this is CGI.redirect_url. When using Apache URL rewriting, that value will contain the original request URL. So if you rewrite foo.cfm to goo.cfm, you can use cgi.redirect_url to return foo.cfm.