Yes, any wood not leafing-out with the rest of the plant is either too weakened to keep or is already dead, so it can be pruned off. As to what caused the dieback, it's hard to say, but it's likely tied to weather. The significant drought much of Maryland has been experiencing for over a year now may be to blame if it wasn't being monitored for watering needs (even during mild dry spells in winter, given that this is a somewhat moisture-loving species). Stress like drought, high heat, and other factors can predispose many plants to opportunistic infections like Botryosphaeria canker. Shrub-type dogwoods such as this can sucker if the roots are otherwise healthy, so if you wanted to remove the dead branches and give the plant more time, it may produce new stems from the roots later this growing season to begin replacing lost growth.

Miri