Fluch cache on all sites in multisite platform Is there a way to clear cache on all sites in platform by using platform alias? For example, drush @platform_name cc all ? (its multisite setup via aegir).

The problem I am facing with is, when I run that command or the one with @sites, I get a message 


  Could not find a Drupal settings.php file at sites/default/settings.php.


So, I then copied default.settings.php as settings.php (which is by default fully commented out) in sites/default, and then it says 


  Drush was not able to start (bootstrap) the Drupal database.


Which is obvious, as default doesn't have database (Aegir creates all sites in platform as separately and never touches default).

I also tried to delete default folder but Drush is telling me it needs to have settings.php there (even after I cleared drush cache). Drush in question is 8.1.0.
An easy way is via the views bulk operations.
When you select some or all sites you can expand the operations menu at the top, where you should find 'Site: Flush_cache'. It's part of the hosting_tasks_extra module (which is included by default now)

Note that you currently do have to enable the operation in the sites view. See https://www.drupal.org/node/2715945