Real property is not subject to State property tax if the property: is owned by the American Association of Blood Banks, Incorporated; or is leased by the American Association of Blood Banks, Incorporated under a lease of 50 years or more. The property tax exemption under this section only applies to that portion of the property that is necessary for and actually used exclusively for the charitable or educational purposes of the American Association of Blood Banks, Incorporated. The property tax exemption under this section only applies for any taxable year for which a property tax credit for the property described in subsection (a) of this section is granted by the governing body of Montgomery County under § 9-317 of this article.