code: @InterfaceAudience.Public
      public void purge() throws CouchbaseLiteException {
          Map<String, List<String>> docsToRevs = new HashMap<String, List<String>>();
          List<String> revs = new ArrayList<String>();
          revs.add("*");
          docsToRevs.put(documentId, revs);
          database.purgeRevisions(docsToRevs);
          database.removeDocumentFromCache(this);
      }
docs: Purges this document from the database;
  this is more than deletion, it forgets entirely about it.
  The purge will NOT be replicated to other databases.
  
  @throws CouchbaseLiteException