title: index method that responds to format.json keeps getting cached
body: <p>I have a Ruby on Rails website. </p>
  
  <pre><code>class DefinitionsController &lt; ApplicationController
     caches_page :index
     def index
       responds_to do |format|
         format.json { render json: @something}
       end
     end
  end
  </code></pre>
  
  <p>When I hit <code>myapp.host.com/definitions.json</code> I get my json data.
  However when I call a function that uses <code>expire_page :action =&gt; :index</code> I won't get a fresh update of that data, it keeps getting serving the old json file from the <code>public</code> dir. Another url of the website that also gets expired, but is a normal page, does come up fresh then.</p>
  
  <p>I use Rails 3, hosting using Nginx and Passenger. When I run it using <code>rails server</code> it does work ok, so it must be something with Nginx or Passenger.</p>
  
  <p>Is there something special I need to do, like call <code>format =&gt; :json</code> on the <code>expire</code> call?</p>