roles/hostvars-defaults/tasks/main.yml

---
# hostvars-defaults/tasks/main.yml
# Sets default variables in multiple hosts to allow them to accessed on other
# hosts via the hostvars['otherhost']['defaultvar']

- name: List host group specific values of default variables
  debug:
    msg: "{{ item.key }}:{{ item.val }}"
  with_items: "{{ hostvars_defaults_dict }}"

- name: Set hostvars as facts to persist them
  set_fact: {"{{ item.key }}":"{{ item.val }}"}
  with_items: "{{ hostvars_defaults_dict }}"