help forcing cache clear automatically

Thanks for the clarification. In most cases I think your suggestion would be right. But in this case, that's exactly my problem: the cached data is persisting for too LONG, not too short an amount of time.

Here's what I ended up doing, in case it's helpful to others. I created an extremely simple module called cache_refresh. It takes a list of specified pages, and deletes their page cache entries each time that cron is run. I just hard coded the pages into the module; you could modify to allow an admin to enter them under a "settings" page instead...

The following is working for Drupal 5.1 (along with the necessary .info file). Seems like it should work in 4.7 as well (without .info), though I haven't tried it yet...

(Disclaimer: I'm not an expert programmer, and make no guarantees, warranties, or other -ees about the following code. That said, it seems to be working for me...)

// $Id: cache_refresh.module,v 1.0 2007/4/8 08:27:00 i Exp $
 
/**
 * @file
 * Clears page cache entries for specified pages each time cron is run.
 */

/**
* Valid permissions for this module
* @return array An array of valid permissions for the custom_navigation module
*/

function cache_refresh_perm() {
return array('access cache_refresh', 'administer cache_refresh');
} // function cache_refresh_perm

/**
* Implementation of hook_cron()
*/

function cache_refresh_cron()
{

$pages_to_refresh = array('http://domain-name.com/pathtopage', 'http://domain-name.com/node/12', 'path to another page to clear');


/* A wildcard search is done. The page cache table will be searched for paths matching (or _partially matching_) those listed in the array above. Matches are then deleted.

foreach ($pages_to_refresh as $page_to_refresh)
{
cache_clear_all($cid = $page_to_refresh, $table = 'cache_page', $wildcard = TRUE); 
}

/*  I think that it would not work to list the homepage in the array of pages to clear:  the path to the homepage would match every entry in the page cache table in a wildcard search.  So homepage (if you need it cleared) is dealt with separately, using a non-wildcard search. Be sure to include both www.domain-name.tld and domain-name.tld  */

cache_clear_all($cid = 'http://domain-name.com/', $table = 'cache_page', $wildcard = FALSE); 
cache_clear_all($cid = 'http://www.domain-name.com/', $table = 'cache_page', $wildcard = FALSE);


}

[per drupal coding standards, omit the closing '?>' in the actual module ]

Note: you may want to set up an additional cron job that visits each page (using wget, curl, lynx, etc) that has been cleared from the cache shortly after cron.php has been run. That way the page cache will be re-populated before real visitors visit the pages. If it's possible to incorporate that step into this module, that would be even better...