above is ok for removing cookie at end of browser session
if however you want the cookie to expire on script completion try sending the cookies value as '' in the header with same name

    my $cookie = new CGI::Cookie(-name=>'cookie',-value=>'');
    print $q->header(-type=>'text/html', -cookie=>$cookie );
[download]

im not sure about by domain either.. although a perl script on a domain can only effect those cookies set by that domain as far as i can recall