Tangible personal property imported from outside of the United States and held in a foreign trade zone or foreign trade subzone, as defined in title 7, chapter 85, for the purpose of sale, manufacture, processing, assembly, grading, cleaning, mixing or display shall be exempt from Tennessee ad valorem taxation while held in the foreign trade zone or subzone and thereafter, if the property is then exported from the foreign trade zone or subzone directly to a location outside of Tennessee.