select max value from 2 tables (mysql) i have two identical tables: 

+-------------+------------+--------+--------+
| domain      | date       | score  | source |
+-------------+------------+--------+--------+


The table contains a domain name, (us)date, a score (float) and a source (like source A or source B). I need always the information from yesterday for an report. 

But the same domain can be in Table A and Table B with a differed score. If that happens, i need only the higher score. If the score is identical, it doesn't matter which source is used. 

A short example: 

Table A: 

+-------------+------------+--------+----------+
| example.org | 2018-12-12 | 0.98   | source A |
+-------------+------------+--------+----------+
+-------------+------------+--------+----------+
| mydomain.org| 2018-12-12 | 5.09   | source A |
+-------------+------------+--------+----------+


Table B:

+-------------+------------+--------+----------+
| example.org | 2018-12-12 | 2.11   | source B |
+-------------+------------+--------+----------+
+-------------+------------+--------+----------+
| company.com | 2018-12-12 | 9.77   | source B |
+-------------+------------+--------+----------+


In this example, i need the domain example.org from Table B: 
example.org, 2.11
mydomain.com, 5.09
company.com, 9,77 

I have tried it with union and joins but i have not received a correct result. 

Does anyone have an idea? Thank you for your efforts.
You don't need a source or a date in resultset at all. If so, you may use the simplest

SELECT domain, MAX(score) score
FROM (SELECT domain, score FROM tableA /* WHERE date = @date */
      UNION ALL
      SELECT domain, score FROM tableB /* WHERE date = @date */ ) dummy
GROUP BY domain


or (maybe more optimal)

SELECT domain, MAX(score) score
FROM (     SELECT domain, MAX(score) score 
           FROM tableA 
           /* WHERE date = @date */ 
           GROUP BY domain
      UNION ALL
           SELECT domain, MAX(score)
           FROM tableB 
           /* WHERE date = @date */ 
           GROUP BY domain 
     ) dummy
GROUP BY domain