code: public static void clearSizeEstimates(String keyspace, String table)
      {
          String cql = String.format("DELETE FROM %s.%s WHERE keyspace_name = ? AND table_name = ?",
                                     Keyspace.SYSTEM_KS,
                                     SIZE_ESTIMATES_CF);
          executeInternal(cql, keyspace, table);
      }
docs: Clears size estimates for a table (on table drop)