Melt butter in a large saucepan over medium heat. Saute onion and garlic until onion is tender. Whisk in flour, and cook 2 minutes. Stir in clam juice and chicken broth, and bring to a boil. Mix in corn, and season with salt, white pepper, thyme, and cayenne. Reduce heat, and simmer 15 minutes.
Stir in cream, crab meat, and green onions. Heat through, but do not boil once the cream has been added.
