I read through the Investor FAQ at the SIPC website. I did not find any mention that the protection is only for securities that are US-domiciled or for non-US domiciled securities as well. The following are relevant excerpts from the SIPC website.
What SIPC protects:
SIPC protection is limited. SIPC only protects the custody function of the broker dealer, which means that SIPC works to restore to customers their securities and cash that are in their accounts when the brokerage firm liquidation begins.
What are securities:
SIPC protects stocks, bonds, Treasury securities, certificates of deposit, mutual funds, money market mutual funds and certain other investments as "securities." SIPC does not protect commodity futures contracts (unless held in a special portfolio margining account), or foreign exchange trades, or investment contracts (such as limited partnerships) and fixed annuity contracts that are not registered with the U.S. Securities and Exchange Commission under the Securities Act of 1933.
Thank you for any feedback.