Problem with javascript_include_tag with :cache


I'm using the Rails 2 feature for asset packing, but I still can't
figure out how Rails decides when to expire a cached asset package. I'm

<%= javascript_include_tag "prototype", "application", "effects",
                           :cache => "cache/site" %>

in my template, which becomes a

<script src="/javascripts/cache/site.js"

in the HTML. If I now update my_stuff.js, the only way to get the
changes "online" so far was deleting the cache/site.js and restart the
server - which is obviously a little bit rough. I tried to touch every
.js in my javascript dir, I touched the
corresponding RHTML template, no effect. I removed cache/site.js, but
then I get a "No route matches "/javascripts/cache/defaults.js" (which
is fairly understandable on the other hand).

Any idea what's best practice here?