You can't do it for all cookies set at a given domain. You need to refer to each cookie by name and specify an Expired value that's in the past. If all of the cookies you set have a proper Expired time (if it needs one; session-only keys are quite useful), you don't have to worry about deleting it later. (Update: I guess that first sentence wasn't 100% accurate.. you *can* use the list of cookie names that the browser provided your script, but of course this will not include cookies that have a path specified that differs from where your script is located, or for cookies that are off-site.)

Of course, I'm assuming this is a Perl + CGI question.. If you're asking how to delete cookies on your local system, you'd need to iterate through the various files or folders where the cookies are stored and delete them from there. Each browser does it differently. If this is what you're asking for, perhaps somebody else has a better answer.