INPUT = 'oracle.world,peoplesoft.world,home.world,remotelocation.world'

type instance_array_type is table of varchar2(50) 
  index by binary_integer;


procedure CheckInstance([color=red]Instance in instance_array_type[/color],
                        Results  out sys_refcursor) is

begin
   open Results for
     select * 
       from outages
         where instance in ([color=red]Instance[/color]);

end;

I'm using this in other packages but it's not very clean if the data has imbedded commas "," and you are trying to delimit by a comma.  Yes, I could use a different delimiter but you never know if some user will use that in the data.

select value 
  from (select substr(Instance, instr(','||Instance||',', ',', 1, rn),
               instr(','||Instance||',', ',', 1, rn + 1) - instr(','||Instance||',', ',', 1, rn) - 1) value
          from (select rownum rn 
                  from dual 
                    connect by level <= length(Instance) - length(replace(Instance,',','')) + 1))

SQL> create table t as 
  2  select level col1, chr(ascii('A')+level-1) col2
  3  from dual 
  4  connect by level <= 10;

Table created.

SQL> select * from t;
      COL1 C
---------- -
         1 A
         2 B
         3 C
         4 D
         5 E
         6 F
         7 G
         8 H
         9 I
        10 J

10 rows selected.

SQL> declare
  2    var sys.odcinumberlist := sys.odcinumberlist (1,3,4);
  3  begin
  4    for rec in (
  5      select col1, col2 from t where col1 in (select * from table(var))
  6    ) loop
  7      dbms_output.put_line(rec.col1||': '||rec.col2);
  8    end loop;
  9  end;
 10  /
1: A
3: C
4: D

type instance_array_type is table of varchar2(50) 
  index by binary_integer;


procedure CheckInstance(Instance in instance_array_type,
                        Results  out sys_refcursor) is

begin
   open Results for
     select * 
       from outages
         where instance in (select * from table(Instance));

end;

   open Results for
     select * 
       from outages
         where instance in (
                            select  instance
                              from  xmltable(
                                             'ora:tokenize($s,",")'
                                             passing INPUT as "s"
                                             columns
                                               instance varchar2(20) path '.'
                                            )
                           )

select  ename
  from  emp
  where ename in (
                  select  *
                    from  xmltable(
                                   'ora:tokenize($s,",")'
                                   passing 'KING,ALLEN,JONES' as "s"
                                   columns
                                     ename varchar2(20) path '.'
                                  )
                 )
/

ENAME
---------
KING
ALLEN
JONES

SQL>