Keep Duplicate With Highest Score Fuzzy Grouping

I have recently decided to dedupe my data but i am having a problem after running fuzzy grouping with the query on updating which duplicate to keep

_key_in is unique, _key_out is the duplicates so for example:

_key_in , _key_out , name , score , dedupe
1 , 1 , ron , 10 , purge
2 , 1 , ronn , 15 , keep
3 , 3 , john , 5 , keep
4 , 4 , matt , 15 , keep
5 , 4 , mat , 10 , purge
6 , 4 , matt , 15 , purge

I want to keep the _key_out with the higher score by setting the field de_dupe to 'keep' and the remainder to 'purge'. The score can also be the same within a duplicate so in the case it is the same i just need to keep one it doesnt matter which one. The query i have below nearly works but it marks duplicates with the same score as keep.

Code:
UPDATE b
SET b.dedupe_result = 'keep'
FROM
[BusinessListings].[dbo].[MongoOrganisationACTM1Destination] b
INNER JOIN

[Code] ....