Assuming you're using the CGI module (and you are, aren't you?), you want to look at the '-domain' flag for the cookie() method, which allows you to specify the partial domain for which the cookie is valid.

For instance, if you want the cookie to be valid for all your sites *.yourdomain.com, you'll want to use something like this untested code:

use strict;
use CGI qw/cookie/;
my $c = cookie(-name    =>  'foo',
                             -value   =>  'bar',
                             -expires =>  '+3M',
                             -domain  =>  '.yourdomain.com',
                             -path    =>  '/cgi-bin/database',
                             -secure  =>  1
                        );
[download]

Note the need to use '.yourdomain.com' rather than just 'yourdomain.com'.