For purposes of this subchapter, stock in a regulated investment company (as defined in section
851) owned by a nonresident not a citizen of the United States shall not be deemed property within the United States in the proportion that, at the end of the quarter of such investment company’s taxable year immediately preceding a decedent’s date of death (or at such other time as the Secretary may designate in regulations), the assets of the investment company that were qualifying assets with respect to the decedent bore to the total assets of the investment company.