RE: Can We Use One Site Canonicals to Other Web Domains?
To inform Google that you have similar or identical content on multiple domains you can use the rel=canonical tag. It’s your wish to cross-post the content across several domains that you own.
If you have different pages with similar content (for example, a page with both a mobile and a desktop version) or a single page of your website is accessible by multiple URLs then it is treated as duplicate versions of the same page by Google. Therefore to remove the ambiguity Google will choose one URL as the canonical version and crawl that, and all other URLs will be considered duplicate URLs and hence will be crawled less often.
Google will make the choice for you if you don’t explicitly tell Google which URL is canonical. Or if Google considers both pages having same content as of equal weight this might lead to unwanted behavior. If a search engine determines that many URLs serve up identical content, the engine will select a preferred version (often referred to as the “canonical” version) and reduce the value of the other copies.
It will do this for each page for which it finds apparent duplicates, and the canonical version may not be the same domain name for each page. This can cause the search engines to consider your internal linking inadequate and ultimately devalue all your domains.
In your case the domain-1’s page repeated in domain-2 so it’s not a duplicate content in domain-1 or domain-2. One of the worst results you have is – exact same content available on two sites (different domain) has some bad impression in Search Engines.