title: Undo a git merge when it has been pushed
body: <p>How can I undo a merge when I have already pushed to master after merge? 
  Here are my steps: </p>
  
  <ol>
  <li><p><code>git add -A</code></p></li>
  <li><p><code>git commit -m "some message"</code></p></li>
  <li><p><code>git fetch origin master:master</code></p></li>
  <li><p><code>git rebase master (resolve merge conflicts)</code></p></li>
  <li><p><code>git push -f origin my local branch</code></p></li>
  </ol>
  
  <p>I want to go back to the state where i was at step 2</p>