"internal" redirects and caching

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My site is on a virtual server using Apache.

I'm current serving a small welcome page to visitors arriving from
a specific domain, say www.othersite.invalid, by using

  RewriteCond % .*\bothersite\b.*  [NC]
  ReWriteRule .* dirpath/specialwelcome.htm      [R=302,L]

specialwelcome.htm has a link back to the main page of my site.

Instead of using the R flag, I'd like to just serve the specialwelcome
content without redirecting the browser.  I don't know if that's
really possible, and that's what my question is about.

If I simply remove the R flag, the internal redirect happens.  If the
original URL was my main page, though, browsers cache the
specialwelcome content for that URL so when a visitor clicks to get to
the main page, the browser (or other caching mechanism) just shows her
the cached content, not what I want.

All that's expected, and I'm wondering if using a Cache-Control header
is a viable way around it.  As I read RFC 2616 (HTTP 1.1), it looks like
"Cache-Control: no-cache" served with the specialwelcome content should

  If the no-cache directive does not specify a field-name, then a cache
  MUST NOT use the response to satisfy a subsequent request without
  successful revalidation with the origin server.

I'm all for the clarity of "MUST NOT", but I wonder if it's reliable in
the real world (by which I of course mean the WWW).  Will browsers and
caching proxies really always honor it?  And are there still HTTP 1.0
caching proxies in the wild that I'd need to worry about?

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