expunge vs rub out

expunge

verb
  • To erase or strike out. 

  • To eliminate completely; to annihilate. 

  • To delete permanently (e-mail etc.) that was previously marked for deletion but still stored. 

rub out

verb
  • To delete or erase or remove (something) by rubbing. 

  • To kill, especially to murder. 

How often have the words expunge and rub out occurred in a corpus of books? (source: Google Ngram Viewer )