List all ansible hosts from inventory file for a task

For a backup I need to iterate over all hosts in my inventory file to be sure that the backup destination exists. My structure looks like

/var/backups/
            example.com/
            sub.example.com/

So I need a (built-in) variable/method to list all hosts from inventory file, not only a single group.

For groups its look like this

- name: ensure backup directories are present
  action: file path=/var/backups/{{ item }} state=directory
          owner=backup group=backup mode=0700
  with_items: groups['group_name']
  tags:
    - backup