public function delete_all_state($cm) {
        global $DB;

        // Delete from database
        $DB->delete_records('course_modules_completion', array('coursemoduleid'=>$cm->id));

        // Check if there is an associated course completion criteria
        $criteria = $this->get_criteria(COMPLETION_CRITERIA_TYPE_ACTIVITY);
        $acriteria = false;
        foreach ($criteria as $criterion) {
            if ($criterion->moduleinstance == $cm->id) {
                $acriteria = $criterion;
                break;
            }
        }

        if ($acriteria) {
            // Delete all criteria completions relating to this activity
            $DB->delete_records('course_completion_crit_compl', array('course' => $this->course_id, 'criteriaid' => $acriteria->id));
            $DB->delete_records('course_completions', array('course' => $this->course_id));
        }

        // Difficult to find affected users, just purge all completion cache.
        cache::make('core', 'completion')->purge();
        cache::make('core', 'coursecompletion')->purge();
    }