drupal 8 drush re-aggregate CSS
Can’t believe Drupal 8 doesn’t have this built-in. Wonder if advagg adds this?
Anyhow it is possible to use drush evaluate PHP to do it:
drush ev '\Drupal::service("asset.css.collection_optimizer")->deleteAll(); \Drupal::service("asset.js.collection_optimizer")->deleteAll(); _drupal_flush_css_js();'