The meaning of "unified" in "Unified Process" is that a single term is used consistently for a single kind of thing.
The term "domain" should not be used in the introductory sentence on this page. What it is calling "domain" is already extensively referred to as "discipline". The work products on this page are grouped by "discipline" and it should be described as such. Tasks are grouped in OpenUP according to "discipline", that's how it is described on the corresponding page, and "discipline" also is the term used in RUP.
Also, the key word is "grouped", not "organized". The term "organized" means any number of things. What is being done here is specifically *grouping* the items.