ADDENDUM:
A related question would be, what actually defines "foreign income?" For instance, some jurisdictions (ex. UK) don't tax dividends paid to US investors at all. So if a stock you hold is UK-domiciled, does that alone let you count its dividends as "foreign income" for purposes of the numerator of the fraction described here: https://www.irs.gov/individuals/international-taxpayers/foreign-tax-credit-how-to-figure-the-credit
Doing so would effectively pad the amount of credit you're eligible for with respect to taxes paid on all other foreign holdings for which there is withholding tax. This seems fishy, since no foreign tax is involved for the UK-domiciled companies, but far be it from me to turn down a smaller tax bill.
