Helper function for the module file

gistfile1.php

<?php
/**
 * Helper to filter tids on given vocabularies.
 *
 * @param array $tids
 *   array of term ids
 * @param array $vocabularies
 *   array of vocabulary machine names
 *
 * @return array
 *   array of terms that live in one of the given vocabularies.
 */
function _views_flag_context_filter_tids_on_vocabularies($tids, $vocabularies) {
  $query = db_select('taxonomy_term_data', 't')
    ->fields('t', array('tid'))
    ->condition('t.tid', $tids);
  $query->innerJoin('taxonomy_vocabulary', 'v', 't.vid = v.vid');
  $query->condition('v.machine_name', $vocabularies);
  return $query->execute()->fetchCol();
}