This has worked for me:
you need to identify the attribute ids for all global attributes then delete all the values from the
catalog_product_entity_* tables that have the attribute id one of those identified above and the store id field not zero.
DELETE FROM `catalog_product_entity_int`
store_id <> 0 AND
attribute_id IN (
WHERE is_global = 1
Do the same for the tables
Rebuild your indexes when your are done.
Note: The select from
catalog_eav_attribute in the way I wrote it will give you attribute ids for the global category attributes also, but that's not important since in the product tables you don't have category attributes references.
Also, before trying this, backup your database in case I missed something.
Thanks to: https://magento.stackexchange.com/users/146/marius