code: public static synchronized void updateTokens(Collection<Token> tokens)
      {
          assert !tokens.isEmpty() : "removeEndpoint should be used instead";
          String req = "INSERT INTO system.%s (key, tokens) VALUES ('%s', ?)";
          executeInternal(String.format(req, LOCAL_CF, LOCAL_KEY), tokensAsSet(tokens));
          forceBlockingFlush(LOCAL_CF);
      }
docs: This method is used to update the System Keyspace with the new tokens for this node