title: SDWebImage clearing cache
body: <p>I'm displaying a list of icons downloaded from the web with text in a table view. The icons can be changed on server side and I need to replace them as soon as new icons are getting available. I try using the following code:</p>
  
  <pre><code>[imgView setImageWithURL:url placeholderImage:[UIImage imageNamed:@"table_avatar_icon"] options:SDWebImageCacheMemoryOnly];
  </code></pre>
  
  <p>And call <code>[[SDImageCache sharedImageCache] clearMemory];</code> In my refresh callback, but it does not purge the contents of the cache. More to it, even if I close the application and open it again the image is still there.</p>
  
  <p>I found only one way to clear the cache and it is by calling <code>[[SDImageCache sharedImageCache] clearDisk];</code>. Which only works after I close and reopen the app.</p>
  
  <p>How can I force SDWebImage to not to use disk caching?</p>