title: Rails 3 and Devise. Kill current session
body: <p>I got an Rails 3 app that uses Devise. I am just wondering how I can "kill" the current session?</p>
  
  <p>This works but I do not know what it does</p>
  
  <pre><code>Devise.sign_out_all_scopes ? sign_out : sign_out(resource_name)
  </code></pre>
  
  <p>This does not work</p>
  
  <pre><code>current_user = nil
  </code></pre>
  
  <p>This does not work either</p>
  
  <pre><code>session[:current_user] = nil
  </code></pre>