Sometimes, you may notice that a source is included in the Similarity Report that you didn't intend, or there may be a source you think was permissible, and don't want it to contribute to the overall similarity score.
When you are viewing a similarity report, from the sources sidebar, choose a source view.
Sources Overview: A list of the top sources found in the document
All Sources: A list of all sources that have matched in the document.
Excluding from either of these views will also exclude it from the other view
Excluding a sub-domain will only remove the match from that level of the domain. If there are multiple matches, from different parts of a single domain, they will be treated differently.
For example: help.turnitin.com would be a different source to example.turnitin.com