Here's a careful reminder that "public domain" is not a worldwide thing ^^; in fact, very few countries have a public domain.

In some cases, if you try to publish something as "public domain" from a certain country, it is invalid - because their judiciary does not define public domain as anything.

It maybe considered public domain, until you die and someone wants that copyright, in which case the family takes precedent over the estate - full stop.

There's a difference between countries that have common law (US and UK) and those that have civil law (the Nordics), so yeah.

But CC is valid license pretty much everywhere, with a few exceptions.