There's no refresh; however, there are two ways of how to do it (at least, two that I can tell you about): first one is a simple one: drop it and create a new one. Another one requires a few SQL statements and can not be automated - it needs your assistance:
First, create a sequence and select several values:
Now, here's where your assistance is needed - it is you who has to decide the next increment (actually, decrement) value from the sequence current value and use it in the ALTER SEQUENCE command:
SQL> select my_seq.currval from dual;
SQL> alter sequence my_seq increment by -9;
In order to restart it, we'll have to select its next value:
SQL> select my_seq.nextval from dual;
The last step is to reset the original increment value:
SQL> alter sequence my_seq increment by 1;
SQL> select my_seq.nextval from dual connect by level <= 10;
10 rows selected.
Obviously, DROP and CREATE is simpler; however, think twice before you do that - will you, for example, have to GRANT access to the sequence to another user(s)? Is the sequence used to enforce uniqueness and - because of restarting - could cause unique constraint violation?