Unfortunately not all browsers respect the expires directive, you might try the following to add the no cache pragma to the headers when you output the page you want to expire:

tachyon

# if using CGI.pm to generate output try:

print $query->header( -type          => 'text/html',
                      -expires       => '-1d',
                      -Pragma        => 'no-cache',
                      -Cache-control => 'no-cache');

# if directly outputing try:

print <<END_OF_HEADER;
Status: 200 OK
Expires: now
Pragma: no-cache
Cache-control: no-cache
Content-type: text/html

END_OF_HEADER
[download]

This should generate a page expired message when you try to go back. </code>