Web Cache threaten PHP security!!!

Below is what PHP tell us: PHP scripts often generate dynamic HTML that must not be cached by the client browser or any proxy caches between the server and the client browser. Many proxies and clients can be forced to disable caching with 1 2 header ("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); // Date in the past 3 header ("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT"); 4 // always modified 5 header ("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1 6 header ("Pragma: no-cache"); // HTTP/1.0 7 But the truth is if the proxy ignore HTTP cache control the page stays. That's what happened to my web site. When customers use the same proxy which ignore cache control the shopping cart that use the session object may be shared by them! so do the ship info!!! Any other PHP solution available?