Boost + Domain Access + flushing cache I have the Boost and Domain Access modules working correctly. But I've found that if the cache is flushed for one domain it doesn't clear for the others. So if content is added to one, it won't show for others until cron has been run.

Any way to fix this at all?
Saw your post on d.o.: https://www.drupal.org/project/domain/issues/1673650
The suggested fix looks good and should still run:
function MODULENAME_domain_cron($domain) {
  global $base_root;
  if (isset($domain['path'])) {
    $base_root = $domain['path'];
  }
  boost_cron();
}

The error you have there seems strange. The argument should be passed to the hook_domain_cron method ?!?
UPDATE: You still can try to make the argument optional:
function MODULENAME_domain_cron($domain=[])

But I would debug that to find out the real reason ..
How does your code look for mymodule_hook_domain_cron?