The other responses pretty much cover the question, but let
me add that we had caching set up in my University for a
while in the hope that it would reduce traffic on our
network.  It created much confusion because it was
transparent - you really didn't know whether the file you
received was 'fresh' or a cached file, often leading to
confusion because you didn't always get the latest file.
You could force a fresh file with a few extra keystrokes.
We pulled caching out after a few months.

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