In both 3.5 & PF druids also have the "share spells" ability with their animal companion. So if your druid were to get the ability to cast Mind Blank, then yes they would share it.
The caveat being that they can't share spells cast by another caster on the druid, which is the same for all familiars/special mounts/animal companions. Also note that if the Animal companion/familiar moves further than 5ft from its master it looses all shared spells and doesn't regain them when it returns.
So - the long and the short of it is - get Mind Blank cast on your Animal Companion unless you plan to multiclass massively AND keep your Companion right next to you at ALL times.
Mmmm...it has been ages since I played in a team with a druid, much less one able to cast 8th level spells, so I had completely forgotten they had "share spells" too, or that they don't get Mind Blank...
So in a party with a wizard, druid, ranger and paladin the poor wizard would have to cast "Mind Blank" seven times every day (if he can), or risk being ambushed any time they get to sleep (and at 15th level every party has made pretty powerful enemies)...that's tough. I guess that allows the DM a lot of control (he can mount a "scry & teleport" attack on them everytime he wishes,which helps feel the warrior types they are valuable), but also forces him to be lenient (because logically, if you let escape a wizard able to cast 8th level spells, you should expect to receive the visit of a bunch of bound high-level fiends within the week).
Well, I guess you could just make high level spells hard to find, so you can justify the baddie not having "Discern Location".