site_settings_domain
This module provides domain context to site setting entities. (Via the domain-module)
You can add a "fallback" (no domain context), meaning that if no site setting with a more specific domain context exists, there's always some value to show.
You can also choose to not add a fallback, then only the site setting specific to that domain will be returned via the site setting loaders with domain context.
On that note, it's important to choose the correct site setting loader (one with domain context enabled), and also use the newly created site setting blocks with domain context instead of the default site setting loaders and blocks.
If the domain access module is enabled, then editor access is also checked.
Important note This module is still in alpha, not all functionality has been thoroughly tested and bugs certainly will come up, feel free to let me know about them and I'll try to fix it all ASAP.