def METHOD_NAME(sender, **kwargs):
    """Triggers a cache invalidation in parent projects from embedded layers"""
    # only for update
    if kwargs['created']:
        return
    project = kwargs['instance']
    updated_parents = []
    for l in Layer.objects.filter(parent_project=project):
        path = l.project.qgis_file.file.name
        if path in updated_parents:
            continue
        updated_parents.append(path)
        p = Path(path)
        p.touch()
        logging.getLogger('g3wadmin.debug').debug(
            'QGIS Server parent project touched to invalidate cache: %s' % path)