title: Clear CMake's internal cache
body: <p>I am sure there is a simple command for this. </p>
  
  <p>I had installed opencv 2.4.3 manually in /usr/local.</p>
  
  <p>Then I removed it and installed OpenCV 2.4.5 from the arch community(I am using Arch linux) which gets installed in /usr</p>
  
  <p>Now when I try to use OpenCV in a cmake project, cmake returns the old paths from /usr/local.</p>
  
  <p>I did some digging around and found that if remove "CACHE" from the line:
  get_filename_component(OpenCV_CONFIG_PATH ="${CMAKE_CURRENT_LIST_FILE}" PATCH CACHE)
  in /usr/share/opencv/OpenCVConfig.cmake I get the correct path.</p>
  
  <p>This points to my question. How do I clear the cmake cache?I am talking about cmake's internal cache not the application's cache which can be deleted by removing CMakeCache.txt.  Is there  a command? Or where is the cmake cache directory/file located? I am sure there's a simple answer for this.
  I know how to set/unset a CACHE variable, but don't know how to clear the complete cache.</p>