It's up to you, but whatever you choose the SRD (or DMG or MotP) has you covered. In the description of the
Planes there's a section for Magic Traits. This gives several options, of which the most relevant are:
Impeded Magic: when casting a spell you must make a Spellcraft check or the spell fails.
Limited Magic: some spells just don't work. (This can, of course, be combined with the above.)
Dead Magic: treat the entire plane as being under an
antimagic field.
There's obviously no definitive answer as regards our world, so just pick the option(s) that work best for you.