It should be possible to blacklist specific domains or regexes locally or globally for all wikis in a wiki farm. Recent forms of harassment I've witnessed consist on outing individuals, their families, or both; by posting URLs to external sites where the harassed user is either depicted, or information about them can be found, etc.
Using #spamblacklist is not adviceable in this case because its contents are in a public wiki page for all to read and see.
Using #abusefilter will not be satisfactory either, because [at least on Wikimedia] there's no true global abusefilter that applies to all wikis. Moreover while private filters do exist, `abusefilter-view-private` is assigned to all sysops and some other groups not under NDA; making the contents avalaible perhaps to too many people.
Now [[ https://www.mediawiki.org/wiki/Manual:$wgSpamRegex | `$wgSpamRegex` ]] will do what it is being requested; but the main disadvantage is that this needs a deployer to add/remove, among others (although we can try to use this as last resort in the most egregious cases for now) via `PrivateSettings.php`.
As such I propose that either a MediaWiki core private special page (which groups should have read/write access to determine later) or the same feature for #spamblacklist to be created where we can blacklist specific "nonpublic" domains that ain't simple spam.
Thank you.