If you are with a graphic design agency that works with global markets, you may want to try and expand your horizons a bit if you don't know a lot about the cultures you'll be dealing with on a regular basis. For example, if you are doing work for a company that has a strong presence in Japan, you may want to read a little about how the Japanese do business or about their culture in general.
How can this help? Take the example above. The Japanese are a very group-oriented society, and once you learn a bit about that, you can it into consideration when drafting an ad campaign or setting up a Website. This is true for many different cultures as well.
Each part of the world has a unique philosophy and viewpoint, and as the global market expands, understanding the ideas and ideals present in different areas of the world makes you more marketable as a designer. If you can show that you have a basic understanding of the global marketplace, you'll be positioned well to work in the field.