I have opened an SCB account in Singapore. I went in person, armed with my HK SCB Priority statements, proof of identity and address, and they opened one for me. Helpful and efficient. It then took ages and ages to set up a link between the HK and SG SCB accounts, but it happened eventually.
My 2 cents on cross border retail banking:
In terms of intra country transfers, HSBC is the most smooth, with the greatest range of currencies and across the widest scope of countries.
Citi works ok between HK/SG/US, but you can only transfer a very limited number of currencies for free.
SCB was the most difficult to get functional in terms of ease of cross border transfers, and still isn't working very smoothly. Although as standalone banks, SCB HK and SCB SG individually had the best service and nicest staff.
OCBC SG + their HK bank didn't work at all well.
Not sure what I'm going to do for free transfers, when HSBC sells its USA retail business.... possibly use Transferwise to transfer money into the bank account of whatever institutional buys their USA business, but it'll be a total pain.