The Cache-Control general-header field is used to specify directives that MUST be obeyed by all caching mechanisms along the request/response chain. The directives specify behavior intended to prevent caches from adversely interfering with the request or response. These directives typically override the default caching algorithms. Cache directives are unidirectional in that the presence of a directive in a request does not imply that the same directive is to be given in the response.
Note that HTTP/1.0 caches might not implement Cache-Control and might only implement Pragma: no-cache (see section 14.32).
Cache directives MUST be passed through by a proxy or gateway application, regardless of their significance to that application, ...