title: Reset/revert a whole branch to another branches state?
body: <p>I have a branch <em>A</em> and a branch <em>B</em> (and some other branches).</p>
  
  <p>Lets say <em>A</em>'s commit history looks like:</p>
  
  <ul>
  <li>commit 5</li>
  <li>commit 4</li>
  <li>commit 3</li>
  <li>...</li>
  </ul>
  
  <p>And <em>B</em>'s commit history:</p>
  
  <ul>
  <li>some other commit</li>
  <li>commit 4</li>
  <li>merge of other stuff from branch <em>C</em> (into branch <em>B</em>)</li>
  <li>commit 3</li>
  <li>...</li>
  </ul>
  
  <p>Basically what I want is to "delete" all changes made by the commits <em>some other commit</em> and <em>merge of other stuff from branch C</em> to branch <em>B</em>.</p>
  
  <p>I want the working tree of branch <em>B</em> to be exactly the same like branch <em>A</em>'s working tree.</p>
  
  <p>How do I achieve this?</p>