No sé si será esto, pero si no, tiene que ser algo parecido
http://www.php.net/manual/en/functio...iter.php#82925 Cita: Note, however, that the Pragma: no-cache header was not intended for this. According to the HTTP 1.0 and 1.1 specifications, this header is defined in the context of a request only, not a response, and is actually intended for proxy servers that may prevent certain important requests from reaching the destination Web server. For future applications, the Cache-Control header is the proper means for controlling caching.
For this reason, watch out when using the Pragma: no-cache with https and IE