Foreign wills are those which are filed in a state other than that in which the real property lies. They create a problem because those probate courts don’t have any jurisdiction over the property located in the state in which you are working.
If your employer/client asks you to cure title that involves foreign wills, it will generally involve recording authenticated/certified/exemplified copies of the foreign probate proceedings in the county where the property lies. The exact process varies from state to state, so, as always, make sure to familiarize yourself with the specific requirements of your state.
If a decedent died intestate, then an affidavit of heirship is the document that you need.