Using the expires header is not always sufficient, if only because of clients that have their clock set wrong. I have had good results with the following headers, which is what the Apache API r->no_cache emits: 
Cache-Control: no-cache
Pragma: no-cache

[download]
in combination with the <code>expires now<code> header you already send out.

In reply to Re: http header / browser caching issues by echo
in thread http header / browser caching issues by d_i_r_t_y

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