They can hold it for any legitimate reason, including any reason that you've consented to in your employment contract. There are various ways which you can transfer outside of the EEA without consent of a data subject, all of which require the principle of maintaining the same level of protection as in the EEA. That being said there is no harm in you requesting them to delete any data that they no longer require...
I asked much the same question to Data Protection Commissioner (or maybe his 2nd in command) during a lecture back around 95/96. Basically HR information in Multinationals been stored on computers overseas. He hemmed and hawed and basically said it was not covered by the Data Protection Act, so they could do what they liked with it.