At its essence, project management is about managing resources and activities towards production of defined deliverables within a specified period of time. What the deliverables are, and what the environment is, should make no difference. Managing a project requires skills and abilities that are generic and applicable to any project.
However ... this is only true if we are free to take a purist approach to project management! In real life, project managers are often (usually?) expected to take on responsibilities that strictly should not be theirs.
If business people (the project director, for example) abdicate some of their responsibilities, it is often the project manager who has to take up the slack in order to ensure project success (generally, this will go unrecognised). In which case, a knowledge of the business would be more than a little helpful. The same is true on the IT side of things.
Project managers will tend to specialise in a particular business field, or on IT projects, or both. It is highly likely therefore, in the light of their deep and broad experience, that they will chose (consciously or otherwise), or be given, responsibilities beyond the pure project management role.
Almost nothing is black and white in this life. Project management (and IT) almost always requires compromises between many (often opposing) factors.
I find myself often answering questions with "it depends", and this topic's question gets the same answer from me. Whilst this can sometimes be an irritating answer, it does I think show an appreciation of the realities.
If you are a purist project manager, you need know nothing about IT or the business. If you have responsibilities in either realm, then you will need to know about it, and may well fail if you do not.
The purist situation is rare, so perhaps I am edging towards "yes, you must have domain knowledge", but ... it really just depends!