For a row in v$bh whose obj 4294967295 , it might be from segment header, file header or undo data.
But I find an interesting block which comes from table MGMT_AVAILABILITY_MARKER (of owner SYSMAN), in the v$bh, the objd displayed is 4294967295.
Neither the OBJECT_ID or DATA_OBJECT_ID of that table is 4294967295 based on dba_objects.
SQL> select unique file#,block# from v$bh where objd=4294967295 and block# not in(2,3) and file# not in (2,7) order by 1;
FILE# BLOCK#
---------- ----------
1 9
1 1658
1 1674
3 4376
3 4392
3 22951
3 23087
3 23088
3 23093
3 23632
3 23656
3 23672
3 25318
3 26479
3 29040
3 30563
3 30769
3 30770
3 30771
3 30999
FILE# BLOCK#
---------- ----------
3 31521
3 31522
3 31523
3 31690
3 32249
3 32411
3 33041
3 33046
3 33150
3 33854
3 34091
3 34093
32 rows selected
Check the a block whose file_id is 3 and block_id is 22951
SQL> select * from dba_extents b where b.file_id=3 and 22951 between b.block_id and b.blocks+b.block_id;
OWNER SEGMENT_NAME PARTITION_NAME SEGMENT_TYPE TABLESPACE_NAME EXTENT_ID FILE_ID BLOCK_ID BYTES BLOCKS RELATIVE_FNO
------------------------------ -------------------------------------------------------------------------------- ------------------------------ ------------------ ------------------------------ ---------- ---------- ---------- ---------- ---------- ------------
SYSMAN MGMT_AVAILABILITY_MARKER TABLE SYSAUX 0 3 22945 65536 8 3
SQL> select object_id,data_object_id from dba_objects where object_name='MGMT_AVAILABILITY_MARKER';
OBJECT_ID DATA_OBJECT_ID
---------- --------------
49853 49853
SQL>