While this affects more models in Katello where every model must be silo'd within an Organization, this problem arises in Foreman as well. Thus, a general use validator that lives in Foreman would be the ideal solution.

Foreman Case:
1. Ensure you have a host and a smart proxy
2. Assign host to organization 'Org A'
3. Assign smart proxy ONLY to organization 'Org B'
4. Ensure 'Org A' does not have any smart proxies
5. Note that UI will not present options to set the Puppet CA for the host on the edit screen
6. Via the API:
PUT to /api/v2/hosts/1 { 'puppet_proxy_id': 1 } (the ID of the smart proxy in 'Org B')
7. Smart proxy that is only in 'Org B' will be assigned to host in 'Org A'

Katello Example:
1. Create Product in 'Org A'
2. Create GPG Key in 'Org B'
3. Via the API:
PUT to /katello/api/v2/products/1 - { 'gpg_key_id': 1} (the ID of the gpg key)
7. Gpg Key from another organization can be assigned to product